Helium-Induced Degradation in the Weldability of an Austenitic Stainless Steel

Autogenous gas tungsten arc welding was performed on helium doped Type 316 (UNS 531600) stainless steel. Helium was uniformly implanted in the material, using the tritium trick, to levels of 27 and 105 appm. Severe intergranular cracking occurred in both fusion and heat-affected zones (HAZ). Microstructural observations of the fusion zone indicated that the pore size, degree of porosity, and tendency to form cracks increased with increasing helium concentration. Scanning electron microscopy showed that cracking in helium doped materials was due to the precipitation of helium bubbles on grain boundaries and dendrite interfaces. This study's results demonstrate that using conventional welding techniques to repair materials degraded by exposure to radiation may be difficult if the irradiation results in the generation even of rather small amounts of helium.